Underwater well structure

ABSTRACT

A substantially cylindrical container has opposite ends one of which is at least partially closed and the other of which is open. The container has an interior sized to receive entirely therein a blowout preventer and associated equipment related to the drilling of oil and gas wells at submerged locations. The one end of the container carries cutting means which are operable upon rotation of the container to penetrate an earth formation engaged by the cutting means. Means are provided for rotating the container about its axis and for circulating fluid under pressure through the one end of the container for removing cuttings from the cutting means.

United States Patent 1191 Rininger Mar. 12, 1974 [54] UNDERWATERYWELLSTRUCTURE FOREIGN PATENTS OR APPLICATIONS lnvefltorl Paul Rininsel',Westlake Village, 1,118,944 7/1968 Great Britain 166 .5

Calif.

[73] Assignee: Global Marine Inc., .Los Angeles, Primary EXaminrMal"/i"Champion C lif Assistant ExaminerRichard E. Favreau Filed: O 1971Attorney, Agent, or Firm-Christie, Parker & Hale [21] Appl. No.: 191,71257 ABSTRACT A substantially cylindrical container has opposite ends U-Cl 1 one of which is at least partially closed and the other [51] Int.Cl E21b 48/01 of which is open. The container has an interior sized [58]Field of Search 175/5-9; t receive entirely therein a blowout preventer'and as- 166/5, 1316- 41 sociated equipment related to the drilling ofoil and gas wells at submerged locations. The one end of the [56] IReferences Cited container carries cutting means which are operableUNITED STATES PATENTS upon rotation of the container to penetrateanearth 3,344,612 10 1967 Rininger 175 9 x by the cutting P are 2,622,40412 1952 Rice 175/8 x Provlded for rotatmg the comamer am and 2,988,1446/1961 Conrad 166/.5 for circulating fluid under Plressure through theone 3,032,106 5/1962 Focht et al v 166/.5 end of the container forremoving cuttings from the 3,202,218 8/1965 Watts et al 175/9 X cuttingmeans. 3,247,672 4/1966 Johnson 166/.5 X 3,352,357 11 1967 Van Eek166/05 35 Claims, 12 Drawlng Figures AYAV iv 1M i IIlIIIIIIVQ Q IIIIIIWM 1 \ll, l l. l 35 /5 PATENIEDIAR 1 2 mm s'amaure PATENIED MR '2 I974SHEET 6 [IF 6 UNDERWATER WELL STRUCTURE BACKGROUND OF THE INVENTIONassociated with the wellhead during drilling of the well and duringsubsequent operation of the well is housed in a container disposed belowthe bottom of the water body.

2. Review of the Prior Art US. Pat. No. 3,344,612 describes a caissonuseful during the drilling and subsequent operation of a well at anoffshore location from a floating drilling vessel. A principal purposeof the caisson described in this patent is to artificially lower thebottom of the body of water over the well site so that blowoutpreventers, normally associated with the wellhead during the drillingoperation, may be disposed clear of the bottom of the drilling vesselfrom which drilling operations are carried out. A blowout preventer hassubstantial height and is required in the drilling of offshore wells. Ablowout preventer is a mechanism for sealing off the well in the eventthat high pressure oil or gas pockets are encountered in the earthformation being drilled. Floating drilling vessels conventionally have acenterwell through the hull thereof through which the drillingoperations are performed from a drilling rig mounted to the vessel overthe centerwell. In areas where shallow water exists, the height of theblowout preventer may be greater than the vertical distance between thewellhead and the bottom of the floating drilling vessel; where thissituation exists, the floating drilling vessel is captive to the blowoutpreventer during drilling operations and cannot be removed from the wellsite during a storm or in the event of an emergency.

US. Pat. No. 3,344,612 teaches that, in such shallow water conditions,the bottom of the body of water is artificially lowered by the use of acaisson so that the distance between the wellhead, located at the bottomof the caisson, and the bottom of the drilling vessel exceeds the heightof the blowout preventer. Thus, it is possible for the floating drillingvessel to be removed from the well site in the event of an emergencyprior to installation of a productionvalve assembly (known in theindustry as a Christmas tree) in place of the' in US. Pat. No. 3,344,612is merely to lower the bottom of the body of water sufficiently that theblowout preventer is located below the hull of the drilling vessel; thetop of the blowout preventer stack, as connected to the wellhead duringdrilling operations, may project above the bottom of the body of water.

The caisson illustrated in US. Pat. No. 3,344,612 has the subsidiaryadvantages and utilities of functioning as a housing for partiallyreceiving the Christmas tree upon completion of the well. Accordingly,the Christmas tree for the completed well does not present anobstruction to navigation in the area.

US. Pat. No. 3,344,612 discloses that the caisson described therein maybe placed in position below the water body by circulating fluid underpressure through the lower end of the caisson, either by dischargingwater under pressure through the bottom of the caisson for flow upwardlyaround the walls of the caisson or by sucking up waterthrough the bottomof the caisson. That is, the patent teaches that the caisson may be usedto advantage only in instances where the bottom of the body of water isdefined by a layer of mud or silt so that fluid circulation or jettingtechniques may be relied upon to install the caisson.

Substantial reserves of oil and gas are known to exist, or are believedwith a reasonable degree of certainty to exist, at underwater locationsadjacent the northern shore line of Alaska and Canada. The slope of theland in these areas is very gradual and continues for many milesoffshore. The result is that substantial fractions of the known orsuspected Arctic oil and gas reserves lie below very shallow bodies ofwater. The caisson described in US. Pat. No. 3,344,612 cannot be used toadvantage because of the peculiarities of the environment in theseareas, all of which lie within the northern polar zone, i.e., north ofthe Arctic Circle.

It is known that on land a thick layer of permafrost exists a shortdistance below the tundra. Permafrost is a layer, often many feet thick,of frozen soil which, because of the presence of soil particles therein,has a hardness considerably greater than that of ice. It is known thatpermafrost extends offshore and under the shallow Arctic lakes and bays.The jetting techniques described in US. Pat. No. 3,344,612 for theinstallation of the caisson described therein cannot be used in theArctic because of the existence of permafrost in the soil formationsunder shallow water.

SUMMARY OF THE INVENTION This invention provides effective, simple,economic and reliable method and apparatus which have all of thebenefits and subsidiary advantages of the caisson described in US. Pat.No. 3,344,612, but are also particularly suitable for use in connectionwith the formation and operation of submerged oil and gas wells in polarzones. Specifically, this invention provides an improved shallow watercaisson which may be installed through permafrost encountered as a partof a soil formation underlying an arctic body of water. The presentcaisson also provides protection from icebergs for the blowoutpreventers and forChristmas trees encountered with submerged oil and gaswells.

In terms of structure, this invention provides apparatus for use insubmerged oil and gas wells. The apparatus includes a substantiallycylindrical container. One of the ends of the container is at leastpartially closed, while the other end of the container is open. Theinterior of the container defines a chamber sized to receive whollytherein a blowout preventer and associated equipment for a desired well.Cutting means are carried by the one end of the container and areoperable upon rotation of the container about its axis to penetrate anearth fonnation engaged by the cutting means. The apparatus alsoincludes means for rotating the container about its axis, and means forcirculating fluid under pressure through the one end of the containerfor removing cuttings from the cutting means.

In terms of method, the container as described above is disposed in asubstantially vertical attitude so that the cutting means carried by thecontainer are disposed at the lower end of the container. The containeris to cause the cutting means to penetrate the earth formation below thewater body in which the oil or gas is being defined. As the container isrotated, it is lowered until the other end of the container is disposedproximate to, and preferably below, the top of the earth formation,i.e., the bottom of the body of water. The container is then secured inposition in the earth formation. The desired well is then drilled in theearth formation through the lower end of the container, the drillingoperation including disposing the blowout preventer and its associatedequipment wholly within the container below the top of the earthformation.

DESCRIPTION OF THE DRAWINGS The above-mentioned and other features ofthe present invention are more fully set forth in the following detaileddescription of presently preferred embodiments of the invention, whichdescription is presented with reference to the accompanying drawing,wherein:

FIG. 1 is a fragmentary cross-sectional elevation view of a drillingvessel floating over a submerged arctic earth formation and illustratesthe problems to which this invention is addressed;

FIG. 2 is a cross-sectional elevation view similar to FIG. 1 showing awell site which includes an improved shallow water caisson according tothis invention;

FIG. 3 is a cross-sectional elevation view of a caisson according tothis invention;

FIG. 4 is a fragmentary cross-sectional elevation view of the lower endof the caisson of FIG. 3 showing the mechanism for rotating the caisson;

FIG. 5 is a bottom plan view taken along lines 55 in FIG. 3;

FIG. 6 is a cross-sectional elevation view of another caisson accordingto this invention;

FIG. 7 is a bottom plan view of another caisson according to'thisinvention;

FIG. 8 is a cross-sectional elevation view taken along lines 8-8 in FIG.7;

FIG. 9 is a fragmentary plan view 99 in FIG. 8;

FIG. 10 is a fragmentary cross-sectional elevation view of anothercaisson according to this invention;

FIG. 11 is a cross-sectional elevation view of a caisson being installedthrough a shield structure previously installed on the bottom of anarctic body of water to receive a plurality of caissons; and

FIG. 12 is a perspective view of a shield structure according to thisinvention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS taken along line FIG. 1illustrates the situation which exists when con-- ventional techniquesfor drilling underwater wells from floating vessels in deep water arefollowed directly in drilling an oil well in shallow water in a polarzone. Thus, a floating drilling platform 10, having a centerwell 11vertically through its hull at a central location, floats in a pool ofwater 12 which results from the formation of an opening 13 in an icesheet 14 covering the surface of a body of water 15. An earth formation16, which includes a layer of permafrost 17, forms the bottom of body ofwater 15; the layer of permafrost is covered by a layer of silt or mud21. The depth of water over the earth formation is shallow in that ablowout preventer 18 mounted to a wellhead structure 19 at the 23 and aconventional rotary table 24 for rotating a string of drill pipe 25which extends through the rotary table and the blowout preventer 18 intowell 20. The drilling rig also includes a drawworks and a travellingblock (not shown) for raising and lowering the string of drill pipe.

It will be observed from an examination of FIG. 1 that drilling platform10 is captive to the well site since blowout preventer 18 has its upperend disposed within centerwell 11. Accordingly, in the event of anemergency or storm, the platform cannot be removed from the well site.Upon completion of the drilling operations at the well, the blowoutpreventer is removed from wellhead structure 19 and a production valveassembly, known as a Christmas tree, is mounted to the wellhead assemblyin the place and stead of the blowout preventer. The vertical height ofthe Christmas tree usually is less than the height of the blowoutpreventer and less than the distance between the wellhead assembly andthe bottom of platform 10. Accordingly, the drilling platform can beremoved from its position over well 20 only upon completion of thedrilling operations following removal of the blowout preventer. Theblowout preventer, because of the existence of governmental regulationsto the contrary, cannot be removed readily from the wellhead assembly atan interim stage during the drilling operations.

FIG. 2 shows that, according to the practice of this invention, blowoutpreventer 18 is located wholly below the top of mud layer 21 within theinterior of a caisson 30 which has an upper end 31 disposed essentiallyat the bottom of body of water 15 as defined by the top of mud layer 21.The caisson is held in position in earth formation 16 by cement 32 whichsurrounds the caisson along substantially its entire length within anannular chamber 33 formed circumferentially of the exterior of thecaisson.

FIG. 2 also shows that the blowout preventer 18 is connected to drillingplatform 10 via a riser pipe 35 which extends circumferentially of drillstring 25 from the top of the blowout preventer to below rotary table24. The upper end of the riser pipe is connected via a suitable duct 36to a drilling mud recirculation system (not shown). As is conventional,high density drilling mud is circulated downwardly through drillstring25 as the string is rotated to form well 20. The injection of drillingmud into drill string 25 is facilitated by the use of a swivel (notshown) connected between the top of the drill string and'the travellingblock (not shown) within the derrick. The drilling mud flows out of theconventional rotary drill bit at the lower end of the drill string andback up through the hole formed by the drill bit. The drilling mudapproaches the lower end of blowout preventer 18 through a length ofsuitably sized casing 37 which extends downwardly from the bottom of thecaisson for a distance which is appropriate to the character of thegeology in which the well is being drilled. The drilling mud flowsupwardly through the blowout preventer around the exterior of the drillstring, and then from the blowout preventer to the platfonn throughriser pipe 35.

Caisson 30 (see FIG. 3) preferably is provided as an elongate, hollow,circularly cylindrical container which is symmetrical about a centralaxis 39. The caisson has a tubular body 40 having an open upper end 31and a lower end 41' which is at least partially closed. In caisson 30,the lower end of the caisson is defined by a conical closure 42 which isconvex downwardly from body 40 and which is integrally connected to thelower end of the body around the circumference of the body. Body 40preferably is defined by a plurality of sections 43, 44, 45 and 46 whichare bolted serially together to form the structure shown. It is alsopreferred that caisson lower end section 43 be of one-piececonstruction, whereas caisson sections 44, 45 and 46 are provided inessentially identical halves 44A, 44B, 45A, etc. Caisson sections 44 and45 are identical; any additional sections of the caisson, required toprovide a caisson having a length greater than that illustrated in FIG.3, would be provided by additional sections essentially identical tosections 44 and 45.

The halves 44A and 44B of caisson section 44, for example, are arrangedso that when they are connected, as by bolts 47, elements 44A and 44Bdefine a portion of the tubular length of the caisson. Accordingly, eachhalf-section element 44A has a wall 48 which is of semi-circularcurvature and which carries a bolting flange 49 along each straight edgethereof; flanges 49 lie within the caisson so that the caisson has asmooth cylindrical exterior surface. To assemble elements 44A and 448 todefine caisson section 44, flanges 49 are mated with each other and areinterconnected by bolts 47. Similarly, each element 44A and 4413includes a flange 50 which extends inwardly from wall 48 along each ofthe opposite semi-circularly curved edges of the wall. Flanges 50 adaptcaisson section 44 to be connected, as by bolts 51, to caisson lower endsection 43 and to adjacent caisson body section 45. The halves 46A and46B of caisson upper end section 46 are identical to halves 44A and 44Band 45A and 45B of sections 44 and 45, respectively, except that thehalves of section 46 do not include flanges 50 in association withcaisson upper end 31.

As will become apparent from the following description, it is the intentof this invention that caisson 30 become a permanent element of well 20.Therefore, it is necessary that the caisson be structured to enable thelargest diameter casing contemplated for well to be passed through thelower end of the caisson. Accordingly, caisson lower end section 43includes a hollow sleeve 53 disposed concentric to caisson axis 39. Thesleeve opens at its lower end 54 through closure 42 at the lower end ofthe caisson. Thus, closure 42 resembles a truncated cone to which thelower end of sleeve 54 is permanently connected, as by welding, at itsinner diameter. Sleeve 53 has an upper end 55 which is locatedintermediate the lengthof caisson lower end section 43. The sleeve isrigidly braced to the cylindrical wall 56 of section 43 by a pluralityof braces 57 which extend radially from the sleeve, adjacent its upperend, to the inner surfaces of wall 56. Preferably braces 57 are definedby I-beam sections or the like and are welded between the sleeve and thewall of caisson section 43. It is also preferred, as shown in FIG. 3,that braces 57 be disposed closely adjacent to sleeve upper end 55 andcarry a circular floor plate 58 which seals the annulus between sleeve53 and wall 56.

A landing stump 60 for blowout preventer 18 is mounted to the upper endof sleeve 53 concentric to axis 39. Preferably stump 60 is provided inthe form of a circular sleeve which has an inner diameter at least equalto that of sleeve 53 and which is configured in conjunction with blowoutpreventer 18 and its associated equipment to receive the blowoutpreventer in the conventional manner. Stump 60 is rigidly affixed to thestructure of caisson lower end section 43, as by a lower end flange 61connected to floor plate 58 as by bolting or welding, for example. Astrong and secure connection between stump 60 and the remainingstructure of caisson lower end section 43 is required in order that thetorque necessary to enable installation of the caisson throughpermafrost layer 17 may be transmitted to the caisson from the stump,and also because it may be necessary to support the entire weight ofcaisson 30 from stump 60.

A plurality of L-slots 62 are provided in the upper end of stump 60 atregular intervals around the circumference of the stump. As shown inFIG. 3, each L-slot has an entrance portion 63 aligned parallel tocaisson axis 39 and open to the upper end of the stump. Each L-slot alsohas a locking portion 64 which extends from the lower end of theentrance portion for a selected distance around the circumference of thestump. All of the L-slots provided in stump 60 have their lockingportions 64 extending in the same direction, ie., either clockwise orcounterclockwise, relative to axis 39.

A plurality of hardened cutting teeth 66 are carried by the convexlycurved surface of lower end closure 42. As shown in FIG. 5, the cuttingteeth preferably are disposed along selected regularly spaced radii ofthe closure. The individual ones of teeth 66 may be defined of hardenedsteel or steel alloy, or by diamonds, as desired. Teeth 66 function,upon engagement of the lower end of the caisson with permafrost layer17, to cut through the permafrost as the caisson is rotated about axis39.

To facilitate the removal of cuttings from adjacent cutting teeth 66during installation of caisson 30, a plurality of openings 68 areprovided through caisson lower end closure 42. Preferably, as shown inFIG. 5, openings 68 are located at intervals spaced circumferentiallyand radially of the caisson intennediate the rows of cutting teeth.Openings 68 communicate from the exterior of the caisson adjacent itslower end to a chamber 69 between floor plate 68 and the closure.Chamber 69 is communicated to the interior of sleeve 53 by a pluralityof holes 70 formed through the sleeve between the floor plate andclosure 42. Accordingly, during rotation of the caisson in the processof cutting through permafrost 17, or through a geological formationwhich may lie between the permafrost layer and mud layer 21, acirculating liquid is introduced into chamber 69 through opening andflows through openings 68 to wash cuttings away from teeth 66.

To define well 20 by the use of caisson 30, drilling platform 10 isfirst disposed at the desired location over the intended well site. Thecaisson lower end section 43 is then positioned below rotary table 24over centerwell l1, and the lower end of drill string 25 (which passesthrough rotary table 24) is connected to caisson section 43 via blowoutpreventer mounting stump 60. The connection of the drill string to thestump is accomplished via an adapter 74 (see FIG, 4) which preferably isfabricated of a length of oil well casing having a diametercorresponding to the largest diameter of casing 37 desired in thecompleted well. It will be recalled from the foregoing description thatsleeve 53 of caisson lower end section 43 is sized to permit the passageof such casing through it. Adapter 74 preferably is secured to the lowerend of the drill string via a bell reducer structure or the like.Adapter 74 is connected to stump 60 via a plurality of projections 75which extend radially outwardly from the exterior of the adapter.Projections 75 correspond in number to the number of L-slots 62 definedin the stump and are spaced apart from each other around thecircumference of the adapter according to the spacing of L-slot 62around stump 60. Projections 75 each have a height, i.e., dimensionparallel to the axis of the adapter, which is no greater than, butpreferably approaches, the dimension of locking portions 64 which areparallel to caisson axis 39. Also, projections 75 have a width, Le, adimension circumferentially of the adapter slightly less than thedimension of entrance portions 63 around the circumference of stump 60.Thus, slots 62 and projections 75 provide for a bayonet-type releasableconnection between the caisson and the drill string.

As shown in FIG. 4, the adapter is connected to stump 60 by aligning theadapter coaxially with sleeve 1 53 in such manner that projections 75are aligned with the entrance portions of respective ones of L-slots 62.The adapter is then moved axially of the stump until the projectionsreach the bottom of the L-slot entrance portions, whereupon the adapteris turned angularly relative to the stump to move projections 75 intolocking portions 64 of the L-slots. Thereafter, the drill string islowered through rotary table 24 to move the lower end section of thecaisson downwardly through centerwell 1 1. As this occurs, caisson bodysections 44,

' 45 and 46 are connected to caisson lower end section 43 in the mannerdescribed above. In this way, the caisson is built up to the desiredlength and lowered into contact with the silt or mud layer which definesthe bottom of body of water 15. A suitable circulating fluid is thenpumped down through drill string 25 and adapter tube 74 to flow outthrough the lower open end of sleeve 53 and through openings 68 viachamber 69; this occurs as the caisson is rotated in response tooperation of rotary table 24 inthe conventional manner.

. Operation of the rotary table causes the drill string to rotate, whichrotation is in turn transmitted to the caisson via projections 75 andstump 60. Because of the flow of circulating fluid through the lower endof the caisson, penetration of mud layer 21 is relatively easilyaccomplished in view of the jetting action of the discharged circulatingfluid. Therefore, it may be possible to penetrate mud layer 2l withoutrelying upon rotation of the caisson and the operation of cutting teeth7 66. When permafrost layer 17 is reached, however, this jetting actionof the circulating fluid will be ineffective to cause the caisson topenetrate the permafrost layer at a satisfactory rate. At this time,rotation of the caisson is relied upon to cause the caisson to bore intothe permafrost, and cuttings generated by teeth 66 during this processare removed from adjacent the lower end of the caisson by thecirculating fluid. Discharged circulating fluid flows upwardly along theouter walls of the caisson, thereby providing annular chamber 33 (shownin FIG. 2). Penetration of the caisson into and possibly throughpermafrost layer 17 is continued until the open upper end 31 of thecaisson is disposed at or below the top of mud layer 21.

Once the caisson reaches its intended position within earth formation16, drill string 25 and adapter 74 are not immediately removed from thecaisson. instead, suitable cement is pumped down through the drillstring into the adapter to flow out through the bottom of the caissoninto annular space 33 and. back up through space 33 to mud layer '21.Preferably the concrete is sufficiently heavy that it spreads laterallythrough mud layer 21 adjacent the top of the caisson, thereby to definea protective shield 77 which extends horizontally in all directions fora desired distance from the caisson. If the density of the concrete isinsufficient to displace mud layer 21 circumferentially of the upper endof the caisson in the manner contemplated by FIG. 2, then, mud layer 21is dredged out circumferentially of the well site before penetration ofthe earth formation by caisson 30 is commenced; in this way, it isassumed that protective shield 77 will be formed in the desired mannerand will cover the desired area around the caisson. It is desired thatcaisson upper end 31 be flush with or disposed below the upper surfacesof shield 77.

Once the cementing process has been completed,

adapter 74 is removed from the caisson by reverse angular indexing ofthe adapter relative to stump 60 and by raising the drill string clearof the caisson. Blowout preventer 18 is then lowered into its intendedposition wholly within caisson 30 and is connected to stump 60. Afterthe blowout preventer has been installed in the caisson, riser pipe 35is connected between the blowout preventer and the drilling vessel anddrilling operations are carried out in the conventional manner throughblowout preventer 18.

The foregoing description assumes that caisson 30 is maintained coaxialwith drill string 25 during the penetration of earth formation 16 by thecaisson, and this coaxial alignment is achieved by reliance solely uponconnection of the drill string to the caisson via adapter 74 and stump60. The foregoing description also involves the assumption that thetorque necessary to cause cutting teeth 66 to penetrate permafrost 17 istransferred from the drill string to the caisson solely by means ofadapter 74 and pump 60. It may be, however, that additional structure isrequired to maintain the vcaisson coaxial with the drill string and totransfer torque from'the drill string to the caisson during penetrationof the earth formation. Accordingly, as shown in FIG. 3, a positioningand torque transmitting spider 79 is removably connected to caissonupper end 31.

The spider includes a ring 80 sized to slip over the exterior of caisson30 adjacent its upper end, circumferentially of the caisson untilmovement of the ring axially of the caisson is limited by engagement ofthe lower surface of a peripheral flange 81 with caisson upper end 31.Flange 81 projects inwardly of ring 80 around the entire circumferenceof the ring. A guide sleeve 82, which preferably has a diameter equal tothat of stump 60, is supported within ring 80 in coaxial alignment withthe ring by a plurality of braces 83. Braces 83 are disposed radially ofthe spider between the exterior of sleeve 82 and ring 80, and theconnection of the braces to the ring preferably is via flanges 81. Thespider is connected in torque transmitting relation to the upper end ofthe caisson by a plurality of projections 84 which extend radiallyinwardly from ring 80 at regularly spaced intervals around thecircumference of the ring. Projections 84 cooperate with correspondingones of a plurality of L-slots 85 which open to the upper end of thecaisson; L-slots 85 are similar to L-slots 62 and therefore are notdescribed in further detail. Sleeve 82 is adapted to be coupled intorque transmitting and caisson aligning relation to drill string 25 bymeans of a .plurality of L-slots 86 which are formed in the sleeve atregularly spaced locations around its circumference so as to open to theupper end of the sleeve. L-slots 86 cooperate with a correspondingplurality of projections (not shown) similar to projections 75 which maybe carried either directly by the drill string, or upon a separateadapter (similar to adapter 74) carried by the drill string at theappropriate location above adapter 74 or directly by adapter 74 whereadapter 74 has a length great enough to extend through both sleeve 82and stump 60. The locking portions of L-slots 62, 85 and 86 all extendin the same direction about the circumference of caisson 30.

In areas where water is very shallow, or where the hazards of icebergsare great, it may be desirable to lo cate caisson upper end 31 somedistance below the upper surface of shield 77. In such a circumstance,it is preferred to equip spider 79 with a cylindrical skirt (not shown)of the same exterior diameter as ring 80. Where present, the skirt iscarried by ring 80 at its upper end so that the exterior surfaces of theskirted spider define a smooth circular cylinder of desired length. Theskirted spider is maintained in connection with caisson 30 during theabove-described process of pumping concrete into space 33 so as todefine shield 77. Preferably the exterior surfaces of the skirted spiderare coated with a lubricant or other material (such astetrafluorethylene) to which cement 77 deos not bond, therebyfacilitating removal of the skirted spider from the caisson after thecement has set sufficiently to maintain the integrity of the shield.

Also, L-slots 85 may be relied upon to connect a suitable cover to thecaisson after the well drilling operations have been completed and theappropriate Christmas tree has been installed on the completed well,thereby to provide protection to the Christmas tree during production ofoil or gas from the well.

Another caisson 87 according to this invention is illustrated in FIG. 6.Caisson 87, except for the aspects thereof illustrated-in FIG. 6, may beconstructed according to the preceding description of caisson 30 ormaybe constructed to resemble the caissons shown in FIGS. 7 through 8,or FIG. 10, for example'ln caisson 87, connection adapter 74 issufficiently long to extend to within caisson body section 45 where itpasses through a circulating fluid manifold ring 88. Manifold ring 88has an inner diameter which is sized to mate intimately with the outerdiameter of connection adapter 74. The interior of manifold ring 88 isopen to the exterior of adapter 74. The manifold ring is supportedwithin body section 45 by a plurality of circulating fluid ducts 89which extend from the ring to outer ends which communicate through bodysection wall 48 to a circulating fluid discharge manifold 90 carried bythe caisson around its circumference. Manifold ring 88 receivescirculating fluid from the interior of adapter 74 via a plurality ofports 91 formed through the adapter at a position defined along thelength of the adapter such that, when the adapter is connected to stump60, ports 91 register with the interior of the manifold ring. Dischargemanifold ring 90 is provided in a caisson according to this inventionwhere the nature of the geological formation to be penetrated by thecaisson is such as to require additional lubrication between the caissonand the formation during the penetration process.

To facilitate the passage of connection adapter 74 through manifold ring88 (or through spider 79), it may be desirable to size the innerdiameter of adapter 74 to mate with the outer diameter of stump 60, inwhich case projections extend from the inner walls of the adapter ratherthan from the outer walls of the adapter, as shown in FIG. 4.

The caissons shown in the accompanying drawings all provide for passageof a circulating fluid through the lower end of the caisson tofacilitate removal of cuttings generated by the cutting means carried bythe lower end of the caisson. Sea water may be used to advantage as asuitable circulating fluid for cuttings removal. To increase the rate ofpenetration of the caisson through permafrost, it may be expedient touse heated sea water so that the caisson both cuts and melts its waythrough the permafrost. In addition to, or as an alternative to heatingthe circulating fluid, the circulating fluid may be a mixture of seawater and ethylene glycol, for example; ethylene glycol is effective toreduce the melting-point of ice.

FIG. 7 is a view of the lower end 95 of another caisson 96 according tothis invention; caisson 96 is also shown in FIGS. 8 and 9. Caisson 30(shown in FIG. 3) preferably has a lower end defined as a truncatedcone, whereas caisson 96 has a flat lower end. Caisson 96 is adapted foruse in situations where permafrost layer 17 may be extremely hard orvery thick. Caisson 96 may also be used where it is desired to locatethe caisson in an earth formation which includes a stratum of rock, suchas shale, with which the drag-type teeth 66 of caisson 30 may not beused effectively.

Caisson 96 includes a flat closure plate 97 disposed across its lowerend 95. The closure plate is permanently secured around its outercircumference to the cylindrical body of caisson 96. A plurality ofcutter cones 98 are carried by the caisson at its lower end. The cuttercones are of conventional manufacture and are of the type encountered intunneling bits or in large-hole bits, for example. Each cutter cone 98is rotatably mounted between a pair of mounting lugs 99 which dependfrom the underside of the caisson at appropriate locations of theclosure plate. As shown in FIG. 7, several cutter cones 98 are arrangedover the lower end of the caisson in such a manner that all arcs aboutthe center of the caisson pass through at least one cutter cone. Thus,upon rotation of the caisson when its lower end is engaged withpermafrost layer 17, for example, an area equal to the bottom end areaof the caisson will be engaged by the cutter cones during one rotationof the caisson.

A plurality of circulating fluid discharge holes 100 are providedthrough closure plate 97 at selected locations of the plate. Dischargeopenings 100 communicate to the exterior of the caisson from a chamber101 formed within the interior of the caisson at its lower end below afloor plate 102. The floor plate is carried by the upper edges of aplurality of radial braces 103, similar to braces 57, which support ablowout preventer mounting stump 104 coaxially of the interior of thecaisson. Stump 104 is essentially identical to stump 60 except thatstump 104 extends through floor plate 102 to an outwardly belled lowerend 105. Like stump 60, stump 104 defines a plurality of L-slots 62 atuniformly spaced locations around its upper circumference.

As shown best in FIG. 7, the two cutter cones 98' which are disposedclosest to the axis of caisson 96 are carried on respective ones of apair of removable doors 1 1 I07 and 108. Doors 107 and 108, as shown inFIGS. 8

and 9, are held in their closed position to close an opening 109 formedin the central portion of closure plate 97 in line with the axis of thecaisson. Doors 108 and 107 are sized, in cooperation with the innerdiameter of blowout preventer mounting stump 104, so that the doors maybe passed upwardly through the stump once they are released from theirclosed position. Preferably, the minimum dimension of opening 109 islarge enough to permit the largest casing for well to be passed throughopening 109 after doors 108 and 107 have been removed from within theopening.

Doors 107 and 108 are locked in opening 109 by a pair of latchingmechanisms '1 12 and 113, respectively. Latching mechanism 112 for door107 includes a rotatable operating member 114 which extends upwardlyfrom the latching mechanism at a location within the cylinder defined bythe upper portion of blowout preventer mounting stump 104; theinnerdiameter of stump 104 at its upper end is represented by the dashed line115 in FIG. 9. Operating member 114 is arranged to be rotated by asuitable tool brought into engagement with it through the drill stringused to rotate the caisson during penetration of earth formation 16, forexample. Accordingly, operating member 114 is located as close aspossible to the central axis of caisson 96.

Latching mechanism 112 includes a plurality of retractable pins 116which cooperate within apertures defined in corresponding lugs 117mounted to-the upper surface of closure plate 97 adjacent centralopening 109. When pins 116 are engaged with lugs 117, as shown in FIG.9, door 107 is maintained within opening 109 with the lower surface ofthe door essentially flush with the lower surface of closure plate 97.Upon rotation of actuating member 114, however, pins 116 are retractedfrom their engagement with lugs 117 so that the tool used to rotateactuating member 114 may also be used to lift door 107 out of hole 109.Such removal of ,door 107, and similarly of door 108, from opening 109is facilitated by providing an upwardly open bevel around the peripheryof opening 109.

Latching mechanism 113 also includes a plurality of retractable pins 116which cooperate in suitable apertures ina corresponding plurality oflugs 117 carried by the closure plate adjacent opening 109. Latchingmechanism 113 includes an actuating member 118. The workings of latchingmechanism 113 are arranged so that when actuating member 118 is pulledupwardly,

the latching mechanism functions to retract pins 116 thereof from lugs117. Actuating member 118 is connected to latching mechanism 112 by alanyard 119. Accordingly, as door 107 is being raised from its closureposition in opening 109 by movement upwardly through stump 104, lanyard.119 is effective to operate lar to caisson 196 in that it has a flatclosure plate 126 permanently connected to the lower end 127 of theright circularly cylindrical hollow body 128 of the caisson. A blowoutpreventer mounting stump 129, having an inner diameter at least as greatas the outer diameter of the largest diameter casing intended to be usedin defining well 20, is disposed coaxially of caisson. 127 above closureplate 126. A plurality of L-slots 62 are formed in the; upper end of themounting stump. The mounting stump is positioned within caisson by aplurality of braces 130 which extend radially of the caisson between theexterior of the mounting stump and the caisson body above closure plate127. A floor plate 131 is carried by braces 130 and closes the interiorof the caisson between the exterior of the mounting stump and the innerwalls of the caisson body to define a circulating fluid chamber 132between the floor plate and the closure plate.

A hole 133 is formed through the center of closure plate 126 andpreferably has a diameter equal to the inner diameter of blowoutpreventer mounting stump 129. A plurality of cutter cones 98 are mountedby corresponding pairs of mounting lugs 99 to the bottom of closureplate 126 so as to effectively cover the entire area of the closureplate around opening 133. A plurality of circulating fluid dischargeopenings 134 are formed through closure plate 126 from chamber 132 atselected locations of the closure plate. I

Like caisson 96, caisson 125 is especially useful where it is desired tolocate a blowout preventer wholly below the bottom of water body 15 andit is necessary to penetrate an extremely hard or very thick layer ofpermafrost or a layer of rock which lies close to the bottom of body ofwater 15. Accordingly, caisson 125 is connected to a length of drillstring 25 for support of the caisson and for rotation of the caisson byan adapter 137. The adapter is provided in the form of an elongatetri-cone drill bit having an outer diameter sized to mate closely withinmountingstump 129 and closure plate opening 133. The adapter bit 137includes three conical drilling cones 138, only two of which are shownin FIG. 10, mounted to the elongate body 139 of the drill bit in amanner similar to the conventional tri-cone rotary tool bit, such as ismanufactured by Hughes Tool Company. The body 139 of the adapter issufficiently long that when it is connected to the caisson byprojections 140 which cooperate .with L-slots 62, drilling cones 138 aredisposed below cutter cones 98. Adapter 137 is hollow for the passage ofsuitable circulating fluidor drilling mud through the drill string tocones 138 in the manner described above. Also, the body of the adapterdefines a plurality of holes 141 which communicate to the circulatingfluid chamber 132. Thus, a portion of the circulating fluid supplied tothe adapter through the drill string flows into chamber 132 and throughopenings 134 to facilitate removal of cuttings from the teeth of cuttercones 98 in response to rotation of caisson 125.

After caisson 125 has penetrated to the desired depth through earthformation 16, adapter 137 is removed from the caisson by disengagingprojections 140 from a hazard exists that the caisson may be damaged byicebergs or berger bits (small icebergs or pieces broken from icebergs)which often scour tracks several feet deep in the mud and silt coveringthe area where the caisson is installed. The shield serves as adeflector or barrier for such icebergs. Even if the iceberg should dragacross the shield, the presence of the shield around the caissonprevents the caisson from being bent, crushed or tipped.

Shield 77 also provides other advantages independent of the problem oficebergs. The performance of drilling and production operation in andthrough caisson 30, for example, may result in heat being transferred tothe permafrost 17 adjacent the caisson sufficient to thaw thepermafrost. Any appreciable thawing of the permafrost, as within thezone 150 represented by broken lines 151 in FIG. 2, may result insubsidence of the formation around and below the caisson. Suchsubsidence may produce sinking of the caisson in the formation ortilting of the caisson, thereby impairing or preventing continuedoperations.

To overcome the hazards of thermally-induced subsidence of theformation, shield 77 extends circumferentially of the caisson asubstantial distance radially beyond the anticipated limits of zone 150,as shown in FIG. 2. The shield, therefore, provides support for thecaisson from over unthawed permafrost and assures that the installedposition of the caisson does not change even if the permafrost closelyadjacent the caisson should thaw completely. I

FIGS. 11 and 12 illustrate another underwater well structure 155according to this invention. Well structure 155 incorporates a shieldassembly 156 and a plurality of caissons 157 arranged in a predeterminedpattern through the shield. FIG. 11 shows that a number of caissons maybe used in association with a single shield, but it will also beappreciated that a single caisson may be used with shield assembly 156if desired.

I As shown best in FIG. 12, shield assembly 156 is composed of aplurality of slab-like component sections 158 which preferably areprecast of concrete (with or without internal reinforcing) at a remotelocation and carried to the site of the well structure aboard drillingvessel 10. Each of the sections 158, along selected ones of its edges,defines at least one tongue projection 159 and at least one receptacle160. Each projection is arranged to mate, in mortise-and-tenon fashion,within a corresponding receptacle of another section so that the severalsections may be interlocked in the manner shown in FlG. 12 to define thecomplete shield assembly. Those shield sections which define the outerlimits of the shield have their corresponding edges sloped or chamferedupwardly, as at 161, so that the bottoms of passing icebergs and thelike may ride up and over the shield and not become caught on and damagethe shield.

Shield assembly 156 is illustrated as being composed of four sections158, each of which has a caisson receiving hole 163 formed through itcentrally of its length and width. Each hole has a diameter slightlygreater than the outer diameter of a caisson 157 over a major portion ofthe length of the caisson. At its upper end, each hole 163 opens to acircumferential recess 164 formed in the upper surface of the shieldsection concentric to the hole.

Underwater well structure 155 is erected following 6 permafrost layer17. Once the shield has been assembled, the several caissons 157 aredrilled into formation 16, in the manner described above, throughrespective ones of shield holes 163. Each caisson 157 is similar tocaisson 30, for example, (or any of the other caissons described above),in that it may be made up in sections as shown in FIG. 11. Each ofcaissons 157, however, differs from the previously described caissons inthat it includes an outwardly extending flange 166 circumferentially ofits upper end. Flanges 166 are sized to mate within shield recesses 164so that the caissons are hung from the shield after the caissons reachtheir desired positions in formation 16 and before the caissons aresecured in the formation by cement 32 as already described. Once theseveral caissons have been installed in the formation through theshield, the several wells may be drilled and completed as describedabove using conventional procedures. g

It will be understood that where each section of the multisectionprefabricated shield assembly defines a receiving hole for a caisson157, it is desirable that the shield section have sufiicient width andlength radially from the hole to provide the above describedantisubsidence support function for its caisson independently of theother sections of the shield. It will also be understood that two ormore sections of a multi-section shield may cooperate to define thereceiving hole and recess for a single caisson if desired, and that amultisection shield may be provided for use with a single caissonwithout departing from the scope of this invention.

The foregoing explanation of this invention has been presented withreference to the description of presently preferred embodiments of theinvention. These embodiments represent only a few of the many possibleembodiments of the invention. Accordingly, the preceding descriptionshould not be considered as limiting the scope of the invention sinceworkers skilled in the art to which this invention pertains will readilyrecognize that modifications and alterations to the abovedescribedprocedures and structures may be made within the context and spirit ofthis invention.

What is claimed is:

1. a wellhead caisson for submerged oil and gas wells comprisingasubstantially cylindrical container having opposite ends one of whichis at least partially closed and the other of which is open, thecontainer having an open interior sized to receive therein through theopen end of the container a blowout preventer and associated equipment,

cutting means carried by the one end of the container operable uponrotation of the container about its axis to penetrate a consolidatedearth formation and the like engaged thereby,

means for rotating the container about its axis, and

means for circulating fluid under pressure through the one end of thecontainer for removing cuttings from the cutting means.

2. Apparatus according to claim 1 including means disposedcircumferentially of the container intermediate the ends thereof fordischarging fluid along the exterior of the container toward the endsthereof.

3. Apparatus according to claim 1 including means 5 rigidly mountedwithin the container coaxially thereof for releasably receiving anelongate rotatable torque transmitting member engaged therewith throughthe container open end and for transmitting to the container torqueapplied thereto.

4. Apparatus according to claim 3 wherein the rigidly mounted meansprovide a bayonet-type releasable connection to the torque transmittingmember.

5. Apparatus according to claim 3 wherein the rigidly mounted means isdisposed adjacent said one end of the container and is arranged toreceive and support a blowout preventer assembly.

6. Apparatus according to claim 3 wherein the rigidly mounted meanscomprises an open-ended tubular sleeve disposed coaxially within thecontainer adjacent the one end thereof, means cooperating between thesleeve and the container defining a circulating fluid chamber within thecontainer adjacent the one end thereof, and fluid passage meanscommunicating from the chamber in association with the cutting means.

7. Apparatus according to claim 6 wherein said one end of the containeris of conical configuration concentric to said axis to provide anupwardly and outwardly sloping container lower end surface.

8. Apparatus according to claim 7 wherein said cutting means comprise aplurality ofdrag teeth projecting from the container lower end surface.

9. Apparatus according to claim 6 wherein the cutting means comprise aplurality of rotatable cutter cones rotatably mounted to the one end ofthe container and effectively distributed over the closed area of saidone end.

10. Apparatus according to claim 9 including an opening defined throughthe one end of the container and centered on the container axis, thecutter cones effectively covering the one end of the container about theopening.

11. Apparatus according to claim 10 including door means for closing theopening, cutting means carried by the door means, and means forreleasably securing the door means in closure relation to the opening.

12. Apparatus according to claim 6 wherein the means for rotating thecontainer includes said elongate rotatable torque transmitting memberand said member comprises a length of hollow drill pipe, connector meanscarried by the drill pipe for releasably connecting the drill pipe tothe sleeve, and means for communicating the interior of the drill pipeto the circulating fluid chamber.

13. Apparatus according to claim 12 wherein the torque transmittingmember is arranged to extend through the one end of the container to anend thereof when the connector means is coupled to the sleeve, andcutting means carriedby the end of the torque transmitting means.

14. Apparatus according to claim 3 including means releasably engageableto the container open end for cooperating with an elongate torquetransmitting member engaged with the container to maintain a coaxialrelation between the container and the torque transmitting member.

15. Apparatus according to claim 14 wherein means engageable to thecontainer open end is arranged to cooperate with the torque transmittingmember for transmitting torque from said member to the container.

16. In a wellhead for a submerged arctic oil well and the like installedin an earth formation underlying a body of water, the combination of Ya. a hollow container substantially wholly disposed in the earthformation adjacent the upper extent thereof for receiving a blowoutpreventer wholly therein,

b. cement securing the container in the earth formation, and

c. a protective shield for the container, the shield being of selectedthickness andextending radially from the container over the earthformation around the container, the shield and the container cooperatingfor support of the container in the formation independently of thecement.

17. A wellhead according to claim 16 wherein the shield extends radiallyfrom the container over the formation for a distance substantiallygreater than the radius of a zone in the formation circumferentially ofthe container subject to thermal influence in response to operationsperformed in or through the container. 7

18. A wellhead according to claim 16 wherein the margins of the shieldremote from the container are sloped upwardly and inwardly.

19. A wellhead according to claim 16 wherein the shield is definedintegral with the cement and is provided in the wellhead in conjunctionwith providing said cement.

20. A wellhead according to claim 16 wherein the container is installedin the formation through the shield.

21. A wellhead according to claim 20 wherein the shield isprefabricated.

22. A wellhead according to claim 21 wherein the shield is comprised ofa plurality of interlocking slablike sections.

23. A method of installing an oil or gas well at a submerged location inarctic waters in an earth formation which includes a stratum ofpermafrost near the top of the formation comprising the steps of a.providing a substantially cylindrical container sized to receive thereina blowout preventer for a desired well at the submerged location andhaving earth formation cutting means carried by one end thereof, theother end of the container being open,

lowering the container on a rotatable tube in a vertical attitude from afloating vessel into engagement of the cutting means with the earthformation underlying the water at the submerged location, 0. rotatingthe container by rotation of the tube at the vessel to cause the cuttingmeans to penetrate the earth formation,

further lowering the container from the vessel during rotation thereofuntil the other end of the container is disposed proximate the top ofthe earth formation,

e. securing the container to the earth formation, and

f. drilling a well into the earth formation through the lower end of thecontainer, including disposing a blowout preventer and associatedequipment wholly within the container.

24. The method of claim 23 including circulating fluid through the oneend of the container and upwardly along the exterior of the containerduring the rotating and further lowering steps.

25. The method of claim 23 wherein the rotating and lowering steps areeffective to define an annular space around the container in the earthformation, and the securing step is performed by disposing cement insaid space.

26. The method of claim 25 wherein the cement is disposed in the spaceby pumping cement through the one end of the container.

27. The method of claim 23 including forming a protective cement shieldfor the container to a desired depth over the earth formation and for adesired distance laterally around the container.

28. The method of claim 27 including forming the shield aftertermination of the lowering step.

29. The method of claim 28 including forming the shield by flowingcement through the one end of the container, upwardly along the exteriorof the container through the earth formation, and over the formation.

30. A method of installing an oil or gas well at a submerged locationunder a body of water comprising the steps of I i a. providing aprotective shield over the top of an earth formation underlying the bodyof water so that the shield extends a desired distance radially from adesired well site,

b. installing in the earth formation through the shield a containersized to receive therein a blowout preventer for a desired well,

c. securing the installed container relative to the shield, and

d. drilling a well into the earth formation through the lower end of thecontainer, including disposing a blowout preventer and associatedequipment wholly within the container.

31. A method according to claim 30 wherein the earth formation includesa stratum of permafrost, and including providing the shield to extendradially over said stratum from the location of the container for adistance substantially greater than the radius from the container in thestratum of a zone of significant thermal influence associated withoperations performed in or through the container.

32. A method of installing an oil or gas well at a submerged location inarctic waters comprising the steps a. providng a substantiallycylindrical container sized to receive therein a blowout preventer for adesired well at the submerged location and having earth formationcutting means carried by one end thereof, the other end of the containerbeing open and carrying a removable upwardly extending skirttherearound,

b. engaging the cutting means with the earth formation underlying thewater at the submerged location while disposing a container in asubstantially vertical attitude,

c. rotating the container to cause the cutting means to penetrate theearth formation,

d. lowering the container during rotation thereof until the other end ofthe container is disposed proximate the top of the earth formation,

e. securing the container to the earth formation,

f. fonning a protective cement shield for'the container to a desireddepth over the earth formation and for a desired distance laterallyaround the container, said depth adjacent the container being greaterthan the spacing of the other end of the container above the earthformation but less than .the spacing of the skirt above the earthformation,

g. removing the skirt from the container after the shield is formed, andg h. drilling a well into the earth formation through the lower end ofthe container, including disposing a blowout preventer and associatedequipment wholly within the container,

33. The method of claim 32 including coating the exterior of the skirtbefore forming the shield with a material to which the cement does notsecurely bond.

34. A method of installing an oil or gas well at a submerged location inarctic waters comprising the steps a. providing a substantiallycylindrical container sized to receive therein a blowout preventer for adesired well at the submerged location and having earth formationcutting means carried by one end thereof, the other end of the containerbeing open,

b. forming a protective cement shield for the container to a desireddepth over the earth formation and for a desired distance laterallyaround the intended location of the container,

c. engaging the cutting means through the shield with the earthformation underlying the water at the submerged location while disposingthe container in a substantially vertical attitude,

d. rotating the container to cause the cutting means to penetrate theearth formation,

e. lowering the container during rotation thereof until the other end ofthe container is disposed proximate the top of the earth formation andnot appreciably above the top of the shield,

f. securing the container to the earth formation, and

g. drilling a well into the earth formation through the lower end of thecontainer, including disposing a blowout preventer and associatedequipment wholly within the container.

35. In a wellhead caisson for submerged oil and gas wells in which thecaisson includes a substantially cylindrical container adapted to besubstantially wholly disposed in an earth formation under a body ofwater and having opposite ends one of which is at least partially closedand the other of which is'open, the container having an open interiorsized to receive wholly therein through the open end of the container ablowout preventer and associated equipment, the caisson also includingmeans for circulating fluid under pressure through the one end of thecontainer, the improvement comprising cutting means carried by the oneend of the container over the closed area thereof operable in responseto rotation of the container about its axis to penetrate a consolidatedearth formation and the like engaged thereby, the cutting means beingdisposed in as sociation with the fluid circulating means for removal ofcuttings from the cutting means by fluid circulated through the one endof the container, and means for rotating the container about its axisincluding means rigidly mounted within the container coaxially thereoffor releasably receiving an elongate rotatable torque trans-. mittingmember engaged therewith through the container open end and fortransmitting therefrom to the container sufficient torque to produceeffective operation of the cutting means on a consolidated earthformation, the fluid circulating means including the rigidly mountedmeans.

3,796,273 Dated March 12, 1974 Patent No.

Inventor-(s) Paul R. Ri ninger It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 2, line 65 Column 8, lines 11,

Column 9, line 27 Column 17 line 41 Column 18 line 5 (SEAL) Attest:

McCOY M. GIBSON, I JR. Attesting Officer Change the comma to a period.

Signed and sealed this 23rd day of July 1974.

C. MARSHALL DANN Commissioner of Patents

1. A WELLHEAD CAISSON FOR SUBMERGED OIL AND GAS WELLS COMPRISING ASUBSTANTIALLY CYLINDRICAL CONTAINER HAVING OPPOSITE ENDS ONE OF WHICH ISAT LEAST PARTIALLY CLOSED AND THE OTHER OF WHICH IS OPEN, THE CONTAINERHAVING AN OPEN INTERIOR SIZED TO RECEIVE THEREIN THROUGH THE OPEN END OFTHE CONTAINER A BLOWOUT PREVENTER AND ASSOCIATED EQUIPMENT, CUTTINGMEANS CARRIED BY THE ONE END OF THE CONTAINER OPERABLE UPON ROTATION OFTHE CONTAINER ABOUT ITS AXIS TO PENETRATE A CONSOLIDATED EARTH FORMATIONAND THE LIKE ENGAGED THEREBY, MEANS FOR ROTATING THE CONTAINER ABOUT ITSAXIS, AND MEANS FOR CIRCULATING FLUID UNDER PRESSURE THROUGH THE ONE ENDOF THE CONTAINER FOR REMOVING CUTTINGS FROM THE CUTTING MEANS. 2.Apparatus according to claim 1 including means disposedcircumferentially of the container intermediate the ends thereof fordischarging fluid along the exterior of the container toward the endsthereof.
 3. Apparatus according to claim 1 including means rigidlymounted within the container coaxially thereof for releasably receivingan elongate rotatable torque transmitting member engaged therewiththrough the container open end and for transmitting to the containertorque applied thereto.
 4. Apparatus according to claim 3 wherein therigidly mounted means provide a bayonet-type releasable connection tothe torque transmitting member.
 5. Apparatus according to claim 3wherein the rigidly mounted means is disposed adjacent said one end ofthe container and is arranged to receive and support a blowout preventerassembly.
 6. Apparatus according to claim 3 wherein the rigidly mountedmeans comprises an open-ended tubular sleeve disposed coaxially withinthe container adjacent the one end thereof, means cooperating betweenthe sleeve and the container defining a circulating fluid chamber withinthe container adjacent the one end thereof, and fluid passage meanscommunicating from the chamber in association with the cutting means. 7.Apparatus according to claim 6 wherein said one end of the container isof conical configuration concentric to said axis to provide an upwardlyand outwardly sloping container lower end surface.
 8. Apparatusaccording to claim 7 wherein said cutting means comprise a plurality ofdrag teeth projecting from the container lower end surface.
 9. Apparatusaccording to claim 6 wherein the cutting means comprise a plurality ofrotatable cutter cones rotatably mounted to the one end of the containerand effectively distributed over the closed area of said one end. 10.Apparatus according to claim 9 including an opening defined through theone end of the container and centered on the container axis, the cuttercones effectively covering the one end of the container about theopening.
 11. Apparatus accorDing to claim 10 including door means forclosing the opening, cutting means carried by the door means, and meansfor releasably securing the door means in closure relation to theopening.
 12. Apparatus according to claim 6 wherein the means forrotating the container includes said elongate rotatable torquetransmitting member and said member comprises a length of hollow drillpipe, connector means carried by the drill pipe for releasablyconnecting the drill pipe to the sleeve, and means for communicating theinterior of the drill pipe to the circulating fluid chamber. 13.Apparatus according to claim 12 wherein the torque transmitting memberis arranged to extend through the one end of the container to an endthereof when the connector means is coupled to the sleeve, and cuttingmeans carried by the end of the torque transmitting means.
 14. Apparatusaccording to claim 3 including means releasably engageable to thecontainer open end for cooperating with an elongate torque transmittingmember engaged with the container to maintain a coaxial relation betweenthe container and the torque transmitting member.
 15. Apparatusaccording to claim 14 wherein means engageable to the container open endis arranged to cooperate with the torque transmitting member fortransmitting torque from said member to the container.
 16. In a wellheadfor a submerged arctic oil well and the like installed in an earthformation underlying a body of water, the combination of a. a hollowcontainer substantially wholly disposed in the earth formation adjacentthe upper extent thereof for receiving a blowout preventer whollytherein, b. cement securing the container in the earth formation, and c.a protective shield for the container, the shield being of selectedthickness and extending radially from the container over the earthformation around the container, the shield and the container cooperatingfor support of the container in the formation independently of thecement.
 17. A wellhead according to claim 16 wherein the shield extendsradially from the container over the formation for a distancesubstantially greater than the radius of a zone in the formationcircumferentially of the container subject to thermal influence inresponse to operations performed in or through the container.
 18. Awellhead according to claim 16 wherein the margins of the shield remotefrom the container are sloped upwardly and inwardly.
 19. A wellheadaccording to claim 16 wherein the shield is defined integral with thecement and is provided in the wellhead in conjunction with providingsaid cement.
 20. A wellhead according to claim 16 wherein the containeris installed in the formation through the shield.
 21. A wellheadaccording to claim 20 wherein the shield is prefabricated.
 22. Awellhead according to claim 21 wherein the shield is comprised of aplurality of interlocking slab-like sections.
 23. A method of installingan oil or gas well at a submerged location in arctic waters in an earthformation which includes a stratum of permafrost near the top of theformation comprising the steps of a. providing a substantiallycylindrical container sized to receive therein a blowout preventer for adesired well at the submerged location and having earth formationcutting means carried by one end thereof, the other end of the containerbeing open, b. lowering the container on a rotatable tube in a verticalattitude from a floating vessel into engagement of the cutting meanswith the earth formation underlying the water at the submerged location,c. rotating the container by rotation of the tube at the vessel to causethe cutting means to penetrate the earth formation, d. further loweringthe container from the vessel during rotation thereof until the otherend of the container is disposed proximate the top of the earthformation, e. securing the container to the earth formation, and f.drilling a well into the earth formation through the loWer end of thecontainer, including disposing a blowout preventer and associatedequipment wholly within the container.
 24. The method of claim 23including circulating fluid through the one end of the container andupwardly along the exterior of the container during the rotating andfurther lowering steps.
 25. The method of claim 23 wherein the rotatingand lowering steps are effective to define an annular space around thecontainer in the earth formation, and the securing step is performed bydisposing cement in said space.
 26. The method of claim 25 wherein thecement is disposed in the space by pumping cement through the one end ofthe container.
 27. The method of claim 23 including forming a protectivecement shield for the container to a desired depth over the earthformation and for a desired distance laterally around the container. 28.The method of claim 27 including forming the shield after termination ofthe lowering step.
 29. The method of claim 28 including forming theshield by flowing cement through the one end of the container, upwardlyalong the exterior of the container through the earth formation, andover the formation.
 30. A method of installing an oil or gas well at asubmerged location under a body of water comprising the steps of a.providing a protective shield over the top of an earth formationunderlying the body of water so that the shield extends a desireddistance radially from a desired well site, b. installing in the earthformation through the shield a container sized to receive therein ablowout preventer for a desired well, c. securing the installedcontainer relative to the shield, and d. drilling a well into the earthformation through the lower end of the container, including disposing ablowout preventer and associated equipment wholly within the container.31. A method according to claim 30 wherein the earth formation includesa stratum of permafrost, and including providing the shield to extendradially over said stratum from the location of the container for adistance substantially greater than the radius from the container in thestratum of a zone of significant thermal influence associated withoperations performed in or through the container.
 32. A method ofinstalling an oil or gas well at a submerged location in arctic waterscomprising the steps of a. providng a substantially cylindricalcontainer sized to receive therein a blowout preventer for a desiredwell at the submerged location and having earth formation cutting meanscarried by one end thereof, the other end of the container being openand carrying a removable upwardly extending skirt therearound, b.engaging the cutting means with the earth formation underlying the waterat the submerged location while disposing a container in a substantiallyvertical attitude, c. rotating the container to cause the cutting meansto penetrate the earth formation, d. lowering the container duringrotation thereof until the other end of the container is disposedproximate the top of the earth formation, e. securing the container tothe earth formation, f. forming a protective cement shield for thecontainer to a desired depth over the earth formation and for a desireddistance laterally around the container, said depth adjacent thecontainer being greater than the spacing of the other end of thecontainer above the earth formation but less than the spacing of theskirt above the earth formation, g. removing the skirt from thecontainer after the shield is formed, and h. drilling a well into theearth formation through the lower end of the container, includingdisposing a blowout preventer and associated equipment wholly within thecontainer,
 33. The method of claim 32 including coating the exterior ofthe skirt before forming the shield with a material to which the cementdoes not securely bond.
 34. A method of installing an oil or gas well ata submerged location in arctic waters comprising the steps of a.providing a substantially cylindrical container sized to receive thereina blowout preventer for a desired well at the submerged location andhaving earth formation cutting means carried by one end thereof, theother end of the container being open, b. forming a protective cementshield for the container to a desired depth over the earth formation andfor a desired distance laterally around the intended location of thecontainer, c. engaging the cutting means through the shield with theearth formation underlying the water at the submerged location whiledisposing the container in a substantially vertical attitude, d.rotating the container to cause the cutting means to penetrate the earthformation, e. lowering the container during rotation thereof until theother end of the container is disposed proximate the top of the earthformation and not appreciably above the top of the shield, f. securingthe container to the earth formation, and g. drilling a well into theearth formation through the lower end of the container, includingdisposing a blowout preventer and associated equipment wholly within thecontainer.
 35. In a wellhead caisson for submerged oil and gas wells inwhich the caisson includes a substantially cylindrical container adaptedto be substantially wholly disposed in an earth formation under a bodyof water and having opposite ends one of which is at least partiallyclosed and the other of which is open, the container having an openinterior sized to receive wholly therein through the open end of thecontainer a blowout preventer and associated equipment, the caisson alsoincluding means for circulating fluid under pressure through the one endof the container, the improvement comprising cutting means carried bythe one end of the container over the closed area thereof operable inresponse to rotation of the container about its axis to penetrate aconsolidated earth formation and the like engaged thereby, the cuttingmeans being disposed in association with the fluid circulating means forremoval of cuttings from the cutting means by fluid circulated throughthe one end of the container, and means for rotating the container aboutits axis including means rigidly mounted within the container coaxiallythereof for releasably receiving an elongate rotatable torquetransmitting member engaged therewith through the container open end andfor transmitting therefrom to the container sufficient torque to produceeffective operation of the cutting means on a consolidated earthformation, the fluid circulating means including the rigidly mountedmeans.